48
J. N. BALL AND BRIDGET I. BAKER
alone (Sage, 1967). Confirmation comes from Schreibman’s work ( 1964)
on Xiphophorus, in which the 6 cells, centrally located in the proximal
pars distalis and differentiated very early in life, were strongly hypertrophied and hyperplastic in fish with thyroid tumors. The cavefish,
Caecobarbus, has a quiescent thyroid, and also displays very inactivelooking 6 cells ( Olivereau and Herlant, 1954).
Reference has already been made to the early differentiation of the
TSH cells in P. lutipinna and Xiphophorus, long before the gonadotrops
are differentiated, and these cells also differentiate early in the guppy
(Sokol, 1961) and the cichlid Herichthys (Baker, 1964a). The TSH cells
sometimes exhibit functional changes during the life history. They are
present only in small numbers in trout and the freshwater (pan-) stages
of the salmon, Salmo salar, in correlation with the very low content of
TSH in these glands; however, in the salmon smolt, with a highly active
thyroid, and about to migrate to the sea, TSH cells are numerous and
highly active ( Olivereau, 1963b, summarizing her earlier works). In
Xiphophorus macuZatus, Schreibman ( 1964) described senility changes
in aging females, in which the TSH cells became smaller, with smaller
nuelei, and exhibit degranulation and vacuolization; in the related guppy,
thyroid activity decreases with aging ( Woodhead and Ellett, 1966),
which supports interpretation of the senescence changes in the TSH cells
of Xiphophorus as indicating reduced secretion of TSH. In young
Xiphophorus the TSH cells look much more active. Silver eels exhibit
vacuolization and ultrastructural features of their TSH cells which perhaps indicate a greater activity than in the yellow stage (Knowles and
Vollrath, 1966b)d).
Some collateral endocrine changes have been found to affect the TSH
cells. They were slightly activated after castration in Xiphophorus
( Schreibman, 1964), and another slight suggestion of gonadal influences
on the TSH cells perhaps comes from Olivereau’s finding (1967a) that
the cells are slightly less active in immature female eels than in immature
males (although we do not know that the eel gonads at this stage secrete
sex hormones). In the case of eels brought to sexual maturity by artificial
treatment, the reactions of the TSH cells are difficult to interpret. When
maturation was induced by injections of TSH contaminated with LH, the
regression of the eel TSH cells is probably a response to thyroidal activation induced by the exogenous TSH (Olivereau, 1961); however, in male
eels brought to maturity by human chorionic gonadotrops, the TSH cells
were activated in parallel to activation of the thyroid (Olivereau and
Herlant, 1960), possibly the result of some unknown interplay between
the exogenous gonadotropin and the hypothalamus. The inactivation of
these cells in female eels matured by injecting carp pituitary extracts is
J. N. BALL AND BRIDGET I. BAKER
alone (Sage, 1967). Confirmation comes from Schreibman’s work ( 1964)
on Xiphophorus, in which the 6 cells, centrally located in the proximal
pars distalis and differentiated very early in life, were strongly hypertrophied and hyperplastic in fish with thyroid tumors. The cavefish,
Caecobarbus, has a quiescent thyroid, and also displays very inactivelooking 6 cells ( Olivereau and Herlant, 1954).
Reference has already been made to the early differentiation of the
TSH cells in P. lutipinna and Xiphophorus, long before the gonadotrops
are differentiated, and these cells also differentiate early in the guppy
(Sokol, 1961) and the cichlid Herichthys (Baker, 1964a). The TSH cells
sometimes exhibit functional changes during the life history. They are
present only in small numbers in trout and the freshwater (pan-) stages
of the salmon, Salmo salar, in correlation with the very low content of
TSH in these glands; however, in the salmon smolt, with a highly active
thyroid, and about to migrate to the sea, TSH cells are numerous and
highly active ( Olivereau, 1963b, summarizing her earlier works). In
Xiphophorus macuZatus, Schreibman ( 1964) described senility changes
in aging females, in which the TSH cells became smaller, with smaller
nuelei, and exhibit degranulation and vacuolization; in the related guppy,
thyroid activity decreases with aging ( Woodhead and Ellett, 1966),
which supports interpretation of the senescence changes in the TSH cells
of Xiphophorus as indicating reduced secretion of TSH. In young
Xiphophorus the TSH cells look much more active. Silver eels exhibit
vacuolization and ultrastructural features of their TSH cells which perhaps indicate a greater activity than in the yellow stage (Knowles and
Vollrath, 1966b)d).
Some collateral endocrine changes have been found to affect the TSH
cells. They were slightly activated after castration in Xiphophorus
( Schreibman, 1964), and another slight suggestion of gonadal influences
on the TSH cells perhaps comes from Olivereau’s finding (1967a) that
the cells are slightly less active in immature female eels than in immature
males (although we do not know that the eel gonads at this stage secrete
sex hormones). In the case of eels brought to sexual maturity by artificial
treatment, the reactions of the TSH cells are difficult to interpret. When
maturation was induced by injections of TSH contaminated with LH, the
regression of the eel TSH cells is probably a response to thyroidal activation induced by the exogenous TSH (Olivereau, 1961); however, in male
eels brought to maturity by human chorionic gonadotrops, the TSH cells
were activated in parallel to activation of the thyroid (Olivereau and
Herlant, 1960), possibly the result of some unknown interplay between
the exogenous gonadotropin and the hypothalamus. The inactivation of
these cells in female eels matured by injecting carp pituitary extracts is